Sidransky H, Epstein S M, Verney E, Verbin R S
J Nutr. 1976 Jul;106(7):930-9. doi: 10.1093/jn/106.7.930.
Young rats were force-fed a complete or threonine-devoid diet for 3 days. On the fourth morning, rats of each group were injected intraperitoneally with cycloheximide (150 mug/100 g body weight) or saline with [6-14C]orotic acid 30 minutes later, 2 hours before killing. Incorporation of [6-14C]orotic acid into hepatic RNA fractions (whole homogenate, postmitochondrial supernatant, microsomes, ribosomes, nuclei and soluble) revealed elevated levels (cpm/mg RNA) in rats force-fed the threoninedevoid diet in comparison to those of rats force-fed the complete diet. However, treatment with cycloheximide decreased the incroporation of [6-14C]orotic acid into the hepatic RNA fractions of the rats force-fed the threonine-devoid diet to levels that were similar to those in rats force-fed the complete diet with or without cycloheximide treatment. Studies dealing with nucleoli isolated by sucrose gradients from livers of control and experimental rats revealed heavier nucleoli and more radioactive labeled RNA in nucleoli ([6-14C]orotic acid administered 30 minutes before killing) of rats force-fed the threonine-devoid diet than in those force-fed the complete diet for 3 days. Treatment with cycloheximide decreased the elevated incorporation in the experimental rats. Also, electron microscopic studies revealed that after cycloheximide treatment, the enlarged hepatic nucleoli of the experimental rats became smaller and returned to a more normal pattern, as found in the control rats. The studies suggest that active hepatic protein synthesis is involved in the increased hepatic RNA synthesis in rats force-fed the threonine-devoid diet and that following inhibition of protein synthesis, as induced by cycloheximide, there is a rapid inhibition of the accelerated hepatic RNA synthesis observed in rats force-fed the threonine-devoid diet with a rapid reversal toward a normal level, i.e. toward that found in control rats.
将幼鼠用完全饲料或缺乏苏氨酸的饲料强制喂养3天。在第四天早晨，给每组大鼠腹腔注射环己酰亚胺（150微克/100克体重），30分钟后注射含[6-¹⁴C]乳清酸的生理盐水，处死前2小时注射。与用完全饲料强制喂养的大鼠相比，用缺乏苏氨酸的饲料强制喂养的大鼠肝脏RNA组分（全匀浆、线粒体后上清液、微粒体、核糖体、细胞核和可溶性部分）中[6-¹⁴C]乳清酸的掺入量（每毫克RNA的计数）升高。然而，用环己酰亚胺处理可使用缺乏苏氨酸的饲料强制喂养的大鼠肝脏RNA组分中[6-¹⁴C]乳清酸的掺入量降低至与用或不用环己酰亚胺处理的用完全饲料强制喂养的大鼠相似的水平。对通过蔗糖梯度从对照和实验大鼠肝脏中分离出的核仁进行的研究表明，与用完全饲料强制喂养3天的大鼠相比，用缺乏苏氨酸的饲料强制喂养的大鼠核仁更重，核仁中放射性标记的RNA更多（处死前30分钟给予[6-¹⁴C]乳清酸）。用环己酰亚胺处理可降低实验大鼠中升高的掺入量。此外，电子显微镜研究表明，用环己酰亚胺处理后，实验大鼠增大的肝脏核仁变小并恢复到更正常的形态，如同对照大鼠中的那样。这些研究表明，在用缺乏苏氨酸的饲料强制喂养的大鼠中，活跃的肝脏蛋白质合成参与了肝脏RNA合成的增加，并且在用环己酰亚胺诱导蛋白质合成抑制后，在用缺乏苏氨酸的饲料强制喂养的大鼠中观察到的加速的肝脏RNA合成迅速受到抑制，并迅速恢复到正常水平，即恢复到对照大鼠中的水平。
